Tips for a Statistically Savvy 2013

My print column offers tips, shared by statistics professionals and readers responding to my blog post, for how to make 2013 a more numerically savvy year. Not all the great suggestions could fit in the column, so here are some more, starting with those from readers:

Michael Dean, a senior marketing analyst in Minneapolis, wanted more clarity in weather news and forecasts. “How accurate are the five-, seven-, and 10- day forecasts?” Dean asked. “Can’t someone collect data on the predicted temperature various days in advance, and then see what temperature it ends up being? What is the range of error by the number of days out for the forecast? What times of the year or what regions of the country does this range vary the most? I am thinking I should ignore anything longer than a five-day forecast, but those may be off a lot, too.” (Some of Dean’s questions are answered by the website Forecast Advisor.)

Dave Fitzpatrick, who works in marketing analytics in New York, wants to see more context around other numbers: Percentage changes from the year before, for instance, instead of just presenting raw statistics. “Too often we see aggregate statistics such as simple percentages cited without any context as to their direction and composition,” Fitzpatrick said. “A much more insightful way of communicating statistical results is to cite the percentage change or, better yet, predictive modeling results that can tell us the impact of one variable on another.”

Jeremy Schneider, another marketing-analytics professional, doesn’t want to see averages falsely smoothed out to create arresting statistics. “My pet peeve is when ads or articles cite murder rates or death rates by saying ‘That’s one murder every 10 minutes,’ or, ‘Someone is dying from starvation every five seconds,’ ” Schneider said. “That certainly might be the average murder or death rate but its not like every 10 minutes on the dot someone is dropping dead.” These stats may be used for a good cause, Schneider said, “but the impact is marred in my eyes by making that claim.”

Kelly Jackson, who teaches at Camden County College in Blackwood, N.J., would like to see better practices in charting, where the Y-axis should always start at 0 when possible. “One of the problems my students have is interpreting data and graphs that don’t use ’0′ as the starting point,” Jackson said. “Imagine a graph that starts vertically at 500 and shows bars of height 550 and 600.”

Richard Hoffbeck, a research data analyst in Minneapolis, would like to see more mention of study design in reports about medical research. “I think a small population case-control study done 20 years ago should be weighted differently than a large-scale experimental trial,” Hoffbeck said.

Judea Pearl, director of the Cognitive Systems Laboratory at the University of California, Los Angeles, cites as a statistical pet peeve “the century-old confusion between correlation and causation,” a point he elaborated on in a recent interview with American Statistician News. (Pearl is the father of Daniel Pearl, the Wall Street Journal reporter who was murdered in Pakistan in 2002.)

Brad Carlin, professor and head of biostatistics at the University of Minnesota, mentioned a lesson from the success of Nate Silver, election forecaster for the New York Times: “Never believe in just one poll; always take some sort of average of all the polls you respect.” Other forecasters who also aggregated polls had success in this election cycle.

New York University mathematics professor Sylvain Cappell offered a few tips. Among them: “There’s a widespread disinclination to recognize how often choosing between alternative courses involves making a judicious balance between quantities, and thus making specific numerical formulations to be able to compute the advantageous tradeoff point,” Cappell said. “Recognizing that there are tradeoffs involves qualitative thinking but after that there’s just no short-cut to computing to see where the tradeoff point actually lies.”

Cappell added that sometimes simple computations, not complex ones, can suffice to aid in decisionmaking. “It’s amazing, even in our complex modern world, how many assertions fail simple ‘back of the envelope’ reasonable estimates with elementary computations,” he said.

About The Numbers

The Wall Street Journal examines numbers in the news, business and politics. Some numbers are flat-out wrong or biased, while others are valid and help us make informed decisions. We tell the stories behind the stats in occasional updates on this blog.